I used these before I got my half cage/6pt harnesses. Let me just say, Schroth's 4pts do wonders...

I have had instructors tell me how great the sports seats in the 135i are, especially with our side bolsters. However, after I got the Schroths in, I didn't realize how much I was moving about. These keep you FIRMLY strapped in the seat, offering two main advantages. First, you feel like you are one with the car. It is easier to feel the direction changes because your body isn't shifting like it used to. However, the most surprising advantage I felt was actually what I didn't feel...sore! You may not realize it, but in the stock 3pt belts you shift around a LOT. As a consequence, you end up unconsciously using the your arms and the steering wheel to support yourself. After using these belts, my arm fatigue went down drastically because I was no longer having to support myself mid corner (which also makes it easier to adjust the wheel, since you dont have all that weight pulling on it).

^^^AGREED...my videos are funny as I squirmed around, trying to use the door and center console to keep readjusting my positioning...slidding around, arms sour. My 4-points did wonders for me at the 'ring and it'll take a serious accident to submarine under these belts if both seats and belts are properly tightened.

Mine were custom sewed so the right side clip is secured by the normal belt clip...no seat belt gongs